(a) Field of the Invention
The present invention relates to an automatic piston drive mechanism for use in dispensing flowable compound material through a dispensing orifice of a chamber housing the material.
(b) Description of Prior Art
Various caulking gun structures are known. Most commonly known is the caulking gun structure wherein cartridges having a housing with compound therein and a displaceable rear wall is inserted on a caulking gun support frame. A piston having a pusher head is engaged by a mechanical lever having a handle which is displaced by a hand movement of the user whereby to advance the piston rod to cause the pusher to displace the rear wall of the cartridge to cause the compound therein to be dispensed through a spout in the front wall of the cartridge.
Some disadvantages of this type of caulking gun are that it is difficult to apply a constant pressure on the rear wall of the cartridge whereby to dispense a constant flow of compound through the spout as the pressure on the rod is activated by a hand lever and the force cannot be maintained gradual and constant. Further, when it is necessary to stop dispensing compound and longitudinal displacement of the piston rod is stopped, compound will continue to be dispensed in view of pressure build-up in the cartridge. Still further, there is no provision to indicate the amount of compound left within the cartridge during dispensation thereof. Still further, such caulking gun structures can accommodate standard size cartridges only.